The invention relates to the field of systems for irradiating articles. In particular, the invention relates to article irradiation systems having conveyors.
Radiation is used to treat many types of products or articles. The types of radiation used include, for example, X-rays, gamma rays, microwaves, and electron beams. The types of articles treated with radiation are many and varied. For example, radiation is used to treat silicon chips, polymers, medical devices, and more recently food. The Food and Drug Administration and the Center for Disease Control have both supported the irradiation of food products for controlling or eliminating microorganisms responsible for food poisoning such as Escherichia coli and Salmonella sp.
An irradiation system is disclosed in U.S. Pat. No. 5,396,074 issued to Peck et al. on Mar. 7, 1995. Peck et al. describe a conveyor system that combines an overhead conveyor with a floor mounted conveyor. Article carriers are suspended from the overhead conveyor track. There is a stop or escapement on the overhead track which holds back the lead article carriers and accumulates carriers behind the escapement. A floor mounted load conveyor is located in a 90xc2x0 turn and has xe2x80x9cdogsxe2x80x9d which grab the bottom of the carriers as they are released by the overhead escapement and convey them toward a process conveyer. The load conveyor accelerates then decelerates the article carriers so that they are mutually spaced upon the process conveyor.
According to Peck et al. the article carriers must be spaced apart to prevent contact between adjacent carriers while they traverse the single electron particle beam. It has been thought that contact with adjacent article carriers would substantially detract from the required uniform radiation dosing of an article. Further this spacing concept carried over to design of beam path conveyors, which provided a gap in the conveying chain to avoid radiation of the chain. Peck et al.""s beam pass conveyor or process conveyor is overly complicated. They describe a conveyor system with spacing between articles conveyed in front of the beam path. The process conveyor of Peck et al. has two conveyor claims with a gap in between so that the electron particle beam does not impact a conveyor chain. It would be advantageous to eliminate the gap between articles so that the emitted radiation is fully utilized, and to simplify the beam pass conveyor so that it is a continuous process conveyor.
It would be advantageous to have a simplified irradiation system with a conveyor system that is entirely floor mounted, and having multiple radiation beam paths. Such a system would simplify the tote transfer between conveyors.
Articles that are irradiated by a horizontally oriented beam may need to be rotated and radiated on another side depending on the depth of penetration of a particular type of radiation. For example, radiation from an electron beam may penetrate solid objects only a couple of inches, whereas X-rays may penetrate the same material to a depth of 8 inches or more. Peck et al. describe a conveyor system with a passive rotation system. The article carriers are rotated by a gear rack on the overhead conveyor. The article carriers hang from the overhead track by virtue of a rotatable collar with pins. The rack meets the pins and spins the article carrier as it passes by. The article carrier is then transported past the radiation beam again to irradiate the other side of the carrier. The passive rotation system of Peck et al. uses an extended tab on the collar to indicate whether the carrier has been rotated. There is no active control of the passive rotation device. It would be advantageous to have an irradiation system with a conveyor system that actively rotates articles and avoids the uncertainty of a passive rotation system with an indicator tab.
It is known that a single cyclotron can provide several paths and types of radiation. Peck et al. illustrates a system with only one electron beam path and one conveyor system. It would be advantageous to have an irradiation system with multiple beam paths, multiple types of radiation, and multiple conveyor systems that could be configured to treat different types of articles with different types of radiation.
Proper irradiation of articles requires precise and accurate dosing of articles. One way to ensure accuracy is to measure the speed of the conveyed articles. Peck et al. describe an irradiation system that measures the speed at which articles are being transported past the radiation source and responds by interrupting the radiation source if the speed of the articles is outside a given range. It would be advantageous to have a conveyor system that adjusts radiation intensity in response to speed fluctuations, which are inevitable in conveyor motors to ensure consistent treatment of articles.
Irradiation with X-ray (and to a lesser extent also by electron beams) is subject to side effects. Photons impinging in the center of the product will be scattered elsewhere inside the product, while x-rays impinging near the sides will partly be scattered to the outside of the product, and will be lost. The consequence of this is that the dose may fall off near the sides. Additionally, these side effects affect articles near the top and bottom faces of the totes, where the dose also may fall off.
These side effects create a problem in systems where there is a gap between article carriers on the process conveyor. Articles positioned near the front and back side of the articles carriers may receive a lower dose of radiation as a result these side effects. Additionally, articles positioned near the top and bottom faces of the article carrier may also receive a lower dose of radiation than other articles in the carrier. It would be advantageous to have a irradiation system that minimized these side effects.
Irradiation systems involving conveyors are described herein. In one aspect, the irradiation system includes a radiation source, a first conveyor system and a second conveyor system. The radiation source has at least one beam path that extends substantially horizontally from the radiation source and at least on beam path that extends substantially downward from the radiation source. The first conveyor system transports articles from a loading area, through the horizontal beam path to an unloading area. The first conveyor system has a process loop for transporting articles through the horizontal beam path one or more times. The process loop has a rotator for rotating the articles around a vertical axes. The second conveyor system transports articles from a loading area, under the downward beam path, to an unloading area. The second conveyor system has a process loop to transport articles under the downward beam path one or more times.
The radiation system may be configured so that the horizontal beam is an X-ray beam and the downward beam is an e-beam. The process loop of any of the conveyor systems may include a roller flight conveyor adjacent to a beam pass conveyor. The roller flight conveyor precedes the beam pass conveyor and travels at a faster rate of speed than the beam pass conveyor and the beam pass conveyor transports articles through a horizontal beam path or under a downward beam path. The articles may be positioned on the beam pass conveyor so that there is little or no gap between articles. The beam pass conveyor may have a continuous chain in the beam path that is a flat top chain or an extended pin chain. The irradiation system may include totes or trays for transporting articles on the conveyors. The conveyor systems may be floor mounted. The irradiation system may include an upper level and a lower level with the first conveyor system located on the upper level and the second conveyor system located on the lower level. If the system includes an upper level and a lower level, a lowerator can be included for lowering trays from the upper level to the lower level and an elevator may be included for raising trays from the lower level to the upper level.
In another embodiment the irradiation system includes a radiation source, a conveyor system, and a control device. The radiation source has at least one beam path. The conveyor system transports articles through the beam path. The conveyor system has a roller flight conveyor adjacent to a beam pass conveyor. The roller flight conveyor precedes the beam pass conveyor and travels at a faster rate of speed than the beam pass conveyor. Articles traveling on the faster roller flight conveyor can be slowed when meeting up with articles traveling on the slower beam pass conveyor. The beam pass conveyor transports articles through the beam path on a continuous chain. The control device adjusts beam strength in response to changes in speed of the beam pass conveyor so that consistent dose delivery is achieved.
The beam pass conveyor may be a flat top chain for bearing articles or the beam pass conveyor may be two parallel stainless steel extended pin chains for capturing and bearing articles. Trays or totes may be used to transport articles on the conveyors.
In another embodiment the irradiation system includes a radiation source, a plurality of totes, a conveyor system, a totes stacker, and a tote destacker. The radiation source has at least one beam path. The totes carry articles. The conveyor system transports totes through the beam path. The conveyor system has a process loop to transport totes through the beam path a plurality of times. The tote stacker is in the process loop and stacks totes prior to transporting through the beam path a plurality of times. The totes destacker is in the process loop and separates stacked totes after transporting through the beam path conveyor system.
In another embodiment the irradiation system includes a lower level, a middle level, an upper level, a radiation source, a fist conveyor system, a second conveyor system, and a third conveyor system. The radiation source, located on the middle level, has at least one beam path extending substantially horizontally from the radiation source, at least one beam path extending substantially downward from the radiation source, and at least on beam path extending substantially upward from the radiation source. The first conveyor system, located on the middle level, transports articles from a loading area, through the horizontal beam path, to an unloading area, has a process loop for transporting articles through the horizontal beam path one or more times and has a rotator in the process loop for rotating the articles. The second conveyor system, located on the lower level, transports articles from a loading area, under the vertical beam path, to an unloading area, has a process loop to transport articles under the vertical beam path one or more times. The third conveyor, located on the upper level, transports articles from a loading area, under the vertical beam path, to an unloading area, has a process loop to transport articles above the vertical beam path one or more times.